A new particle sizing device is described for sizing liquid spray drops and "dry" particulates in situ. A pulsing ultra violet laser of short pulse duration is used to illuminate moving particles. "Stop action" images are formed on a vidicon and presented on a TV monitor. These images are stored in an instant replay recorder and replayed in slow motion for sizing manually or by automatic image analysis. This particle sizing device is now standard equipment at the National Bureau of Standards for sizing liquid spray drops. Excerpts from a number of contracts performed by the author are given via 35mm slides and by replay from the instant replay recorder. The mechanics of droplet formation, ligaments, hollow spheres, evaporation, agglomeration, combustion of liquid fuel droplets, impingement, impaction of insecticides on live insects, hairsprays, inhalation and weight respirable of some typical household aerosol and hand pumped sprays are explained, together with an explanation of the techniques of measuring particle velocity.